Method of manufacturing oil-filled cables



1968 ETSUJI KUSAKABE 3,

METHOD OF MANUFACTURING OIL-FILLED CABLES Filed Jan. 2, 1962 United States Patent 3,409,488 METHOD OF MANUFACTURING OIL-FILLED CABLES Etsuji Kusakahe, Kohoku-ku, Yokohama, Japan, assignor to The Furukawa Electric Company Limited, Tokyo, Japan, a corporation of Japan Filed Jan. 2, 1962, Ser. No. 163,663 Claims priority, application Japan, Jan. 17, 1961, 36/ 1,380 1 Claim. (Cl. 156-48) The present invention relates to an improved method for manufacturing oil-filled cables using vacuum drying and impregnating process.

The principal object of the invention is to obviate the disadvantages of the heretofore known methods and provide easily and economically oil-filled cables of excellent quality without secondary drying process and excessive insulating oil.

Oil-filled cables are usually provided with oil passages therein, through which insulating oil of a lower viscosity is forced into the cables.

Prior to the pouring of insulating oil, the cable core is sufficiently dried in a drying vessel and covered with metal sheath, and then the cable is again heated and evacuated to remove the air and moisture from both ends. Insulating oil is then forced inside of the metal sheath to impregnate the cable core.

The above process is hereinafter called the conventional method.

In the conventional method, once dried cable core is exposed to open atmosphere and absorbs air and moisture when the metal sheath is applied thereto, so that, after the metal sheath has been applied, it is dried and evacuated again. In the so-called secondary drying process air and moisture are removed from each end of the cable so that, though the portion near each end can be dried easily, yet the central portion is very difiicult to dry, and, moreover, it requires a long time, and, because a perfect drying is almost impossible, the length of cable to be manufactured is limited, and particularly when lead is used for metallic sheath, the lead covering is heated to a temperature of 100 to 120 C. for a long time, so that the grain size of lead grows to locally reduce the mechanical strength and considerably reduce the durability of the cable.

In order to avoid the above disadvantages, there has been proposed a process of drying the cable core in a drying vessel, filling the vessel with insulating oil to impregnate the cable core, and covering the core with metal sheath by a press as it is applied with oil pressure without being exposed to the atmosphere, and such process is usually referred to as a mass impregnation method. But this method necessitates a large quantity of insulating oil and a large-capacity device for treating insulating oil as the drying vessel is filled with refined insulating oil.

In order to obviate the above disadvantages, the present invention provides an improved process of manufacturing oil-filled cables which needs no secondary drying process and is much more economical than the socalled mass impregnation method.

The cable core may be dried by heating in a conventional heating oven, or if desired, in a vacuum vessel provided with a suitable heating means at the same time of vacuum drying.

For a better understanding of the invention, reference is made to the accompanying drawings, in which,

FIG. 1 is a diagrammatic view of a device for carrying out the invention,

FIG. 2 is a diagrammatic sectional view of a press and FIG. 3 is a diagrammatic view of the other device for carrying out th invention.

Referring to FIGS. 1 and 2, 1 represents such a single cable core wound with an insulating tape or such a set of three cores that is wound around a revolving drum 3 in a totally enclosed drying vessel 2 which is connected to a vacuum pump 4 through a pipe and valve a. The outlet opening 2' of the vessel is sealed by means of a packing 6 and the vessel is connected by means of a detachable joint pipe 8 with a press 7. In order to lead out the cable core through the outlet opening of the vessel 2 the end of the cable core is connected previously with a piece of metal 5 and a pull-out wire 9. Packing 6 is so constructed as to allow the core, when pulled out of the vessel, freely to pass through it. After the vessel 2 has been made air-tight it is evacuated by the vacuum pump 4 to remove air and moisture from the cable core. After the cable core 1 has been dried, it is passed through the joint pipe 8 to the press 7 under the vacuum condition. In order to facilitate the above operation a detachable joint pipe 8 is provided between the outlet opening of the vessel 2 and the nipple holder 10 of the press 7. After the pull-out wire 9 is passed through the nipple holder 10, nipple 11 and die 12 in the press 7, the press is operated shortly to enclose the end of the Wire 9 with metal sheath 13, the end of which is collapsed to tightly seal the wire end and a pipe 18 with a valve 14 is connected to the sheath for the purpose of feeding insulating oil into the cable. Then the inside of the pipe 8, nipple holder 10, and the metal sheath 13 is evacuated by the vacuum pump 4 by opening the valve b, and the press 7 is continuously operated to extrude the metal sheath 13, the inside of the sheath being kept under vacuum. Thus the sheathed cable is wound upon a wind ing drum to complete the press operation. After its completion, the rearward end of sheath is tightly sealed by a suitable means and the valve 14, secured to the end of the sheath, is connected with an oil feeding device to supply insulating oil inside the sheath and to impregnate the cable core. The above process has an advantage that, if insulating oil is fed while the inside of the sheath is being kept under vacuum by means of a vacuum pump connected to its end, it fills up the inside of the sheath, thereby facilitating impregnation of the cable core.

The present invention may be also carried out by a device shown in FIG. 3, in which the same parts as, or similar parts to, those shown in FIG. 1 are represented by the same reference numerals. Winding drum 15 is mounted on a turning base 16, and 17 is an oil feeding device which is connected to the sheathed cable through an oil pipe 18 and valve 14. The cable core 1 passing through the joint pipe 8 and the press 7 is evacuated by means of the vacuum pump 4 to maintain vacuum condition. Under such condition, the press is continuously operated to cover the cable core with metal sheath 13 and at the same time, insulating oil is supplied inside of the sheath from the oil feeding device 17, so that the cable core may be immediately impregnated with oil, and then the sheathed cable can be wound upon the winding drum 15. During the above pressing and impregnating operations, the vacuum pump 4 is continuously operated to keep under vacuum the joint pipe 8 and the nipple holder 10 of the press so that the cable core may be protected from absorbing air and moisture and also easily impregnated with insulating oil.

According to the method of the invention, as above described oil-filled cables can be manufactured by impregnating the cable core with insulating oil after perfectly drying and covering it with metal sheath or while applying the metal sheath to it and the operation is carried out in the totally enclosed evacuated system including the drying vessel, joint pipe and press without danger of air and moisture entering the core and the impregnation of the core with insulating oil can be carried out effectively without necessitating many days drying as in the conventional method and without limiting the length of cable to be manufactured, and, when lead is used as the metal sheath, the sheathed lead is not heated subsequent to sheathing, so that there occurs no lowering of mechanical strength; it does not require a large quantity of insulating oil or a large-capacity oil treating device as in the mass impregnation method and, therefore, the method under the invention has the outstanding advantages of improving the manufacturing efficiency and simplifying the installations, being capable of easily manufacturing a longer cable of uniform quality.

What I claim is:

1. A method of manufacturing oil-filled cables which comprises drying under vacuum in a drying zone a cable core having paper insulation covering, delivering said covered core after drying from said drying zone to a sheathing zone through a vacuum tight joint pipe, maintaining vacuum conditions in said sheathing zone and covering said cable core with a metal sheathing while said cable core is passed therethrough, sealing the forward end of said sheathed cable upon emergence from said sheathing zone and sealing the rearward end of said sheathed cable at the completion of said sheathing step while under vacuum conditions, thereby providing a hermetically sealed length of interiorly dry sheathed cable which is protected from moisture and gas absorption while awaiting oil-filling; thereafter directly attaching means to said cable leading to its interior for delivery of oil, and filling said hermetically sealed sheathed cable with oil from said means while the interior of said cable is under reduced pressure such as will efiectively induce oil flow thereinto.

References Cited UNITED STATES PATENTS 867,658 10/1907 Hoopes et al. 207-40 2,115,574 4/1938 Gasser 156-48 2,531,156 11/1950 Pierney et a1 15648 X 3,032,464 5/1962 Grieve 156-51 X EARL M. BERGERT, Primary Examiner.

T. R. SAVOIE, Assistant Examiner. 

1. A METHOD OF MANUFACTURING OIL-FILLED CABLES WHICH COMPRISES DRYING UNDER VACUU IN A DRYING ZONE A CABLE CORE HAVING PAPER INSULATION COVERING, DELIVERING SAID COVERED CORE AFTER DRYING FROM SAID DRYING ZONE TO A SHEATHING ZONE THROUGH A VACUUM TIGHT JOINT PIPE, MAINTAINING VACUUM CONDITIONS IN SAID SHEATHING ZONE AND COVERING SAID CABLE CORE WITH A METAL SHEATHING WHILE SAID CABLE CORE IS PASSED THERETHROUGH, SEALING THE FORWARD END OF SAID SHEATHED CABLE UPON EMERGENCE FROM SAID SHEATHING ZONE AND SEALING THE REARWARD END OF SAID SHEATHED CABLE AT THE COMPLETION OF SAID SHEATHING STEP WHILE UNDER VACUUM CONDITIONS, THEREBY PROVIDING A HERMETICALLY SEALED LENGTH OF INTERIORLY DRY SHEATHED CABLE WHICH IS PROTECTED FROM MOISTURE AND GAS ABSORPTION WHILE AWAITING OIL-FILLING; THEREAFTER DIRECTLY ATTACHING MEANS TO SAID CABLE LEADING TO ITS INTERIOR FOR DELIVERY OF OIL, AND FILLING SAID HERMETICALLY SEALED SHEATHED CABLE WITH OIL FROM SAID MEANS WHILE THE INTEIOR OF SAID CABLE IS UNDER REDUCED PRESSURE SUCH AS WILL EFFECTIVELY INDUCE OIL FLOW THEREINTO. 